Myosins are molecular motors that use the energy derived from ATP hydrolysis to mediate actin-based motility. Defects in myosins result in cardiomyopathies, neurological problems, deafness and blindness. Class I myosins are small, single-headed, non-filamentous proteins that have been implicated in cell motility, establishment of polarity, and actin organization. The long-term objective of this project is to determine the cellular function of one particular class I myosin, Myo1c. Specifically, the first aim is to study the localization of endogenous and expressed Myo1c in fixed and live tissue culture cells, and determine where it concentrates during dynamic cytoskeletal events. In the second aim, the effect of knocking down the cellular concentration of Myo1c on cytoskeletal properties and cell movement will be monitored. As a complementary approach, the effect of increasing the cellular concentration of Myo1c or mutated Myo1c on the same cytoskeletal and motile characteristics will be investigated in the third aim. These experiments will test the hypotheses that Myo1c concentrates in cellular regions undergoing rapid rearrangements of the cytoskeleton and mediates dynamic cytoskeletal events at the cell cortex.